Ni-Rich NCM Cathode Composition for Thermal Stability and Output
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Solution Overview
Problem
Ni-rich NCM-based lithium composite transition metal oxides face issues with thermal stability, increased resistance, and long Li ion diffusion paths due to over-calcination, leading to deteriorated output performance and surface rock-salt crystal structures.
Innovation Solution
A positive electrode material comprising a mixture of first and second single-particle-type lithium composite transition metal oxides with specific particle diameters and lithium-to-metals molar ratios, prepared through over-calcination, to enhance thermal stability and reduce side reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If over-calcination is performed to improve thermal stability and reduce side reactions, then thermal stability is enhanced, but Li ion diffusion path increases and output performance deteriorates
Solution Approach 1:
The positive electrode active material is divided into multiple secondary particles, each consisting of multiple primary particles. This segmentation allows the material to benefit from over-calcination (improved thermal stability) while maintaining shorter Li ion diffusion paths through the smaller primary particle structure, thus resolving the contradiction between thermal stability and output performance.
Solution Approach 2:
Different regions of the positive electrode material have different properties: primary particles are small (1-3 μm) to ensure short Li ion diffusion paths and high output performance, while secondary particles aggregate these primary particles to provide overall thermal stability. This local differentiation of particle size and structure allows simultaneous achievement of both thermal stability and high output performance.
2Quantity of substance
If nickel content is increased to enhance capacity, then capacity increases, but thermal stability deteriorates and side reactions increase
Solution Approach 1:
The particle size parameter is changed to 1-3 μm for primary particles, which suppresses side reactions and improves thermal stability of Ni-rich materials. Additionally, the Li/M ratio is optimized to 1.05-1.15 to further enhance thermal stability while maintaining high capacity, thus resolving the contradiction between capacity and thermal stability.
3Device complexity
If single-particle-type material is used to simplify structure, then structure is simplified, but Li ion diffusion path increases and output performance deteriorates
Solution Approach 1:
The material structure is segmented into primary particles (1-3 μm) that are further aggregated into secondary particles. This segmentation maintains structural simplicity while ensuring short Li ion diffusion paths through the small primary particle size, thus resolving the contradiction between structural simplicity and output performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution improves thermal stability, suppresses resistance increases, and enhances output performance by optimizing particle size and lithium content, addressing the limitations of single-particle-type materials.
Implementation Method 1
electric energy is produced by a redox reaction when the lithium ions are intercalated/deintercalated into/from the positive electrode and the negative electrode
Implementation Method 2
a longer Li ion diffusion path than a secondary particle positive electrode material
Data Source
AI summary
The present invention relates to a positive electrode material for a secondary battery, the positive electrode material including a first positive electrode active material and a second positive electrode active material, the first positive electrode active material and the second positive electrode active material being single particle types and lithium composite transition metal oxides including nickel, cobalt, and manganese and having a nickel content accounting for 60 mol % or more of total metals except for lithium, wherein the first positive electrode active material has a mean particle diameter (D50) of 3 μm or less and a molar ratio (Li/M) of lithium to the metals (M) except for lithium of 1.10 to 1.20, and the second positive electrode active material has a mean particle diameter (D50) of greater than 3 μm and a molar ratio (Li/M) of lithium to the metals (M) except for lithium of 1.00 to 1.13.